There is currently no test that can definitively diagnose the disease.

Scientists may have developed a revolutionary eye test that can detect Parkinson’s disease before symptoms surface.

The UCL research team said promising experiments on animals could pave the way for cheap, non-invasive examinations and earlier treatment.

Researchers noticed in tests on rats that retinas developed changes before symptoms developed.

Professor Francesca Cordeiro, who led the research, told the BBC it was a “potentially revolutionary breakthrough in the early diagnosis and treatment of one of the world’s most debilitating diseases”.

“These tests mean we might be able to intervene much earlier and more effectively treat people with this devastating condition.”

One in every 500 people develops Parkinson’s, which is the second most common neurodegenerative disease after Alzheimer’s.

The disease, which is caused by a shortage of dopamine, damages brain cells, causes tremors, muscle stiffness, slowness of movement and a reduced quality of life.

Parkinson’s itself doesn’t kill, but it worsens over time. Currently, no brain scan or blood test can definitively diagnose the disease.

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Dr Arthur Roach, director of research at the charity Parkinson’s UK, told the BBC there was “an urgent need for a simple and accurate way of detecting the condition, particularly in its early stages”.

“Although the research is in its infancy and is yet to be tested on people with Parkinson’s, a simple non-invasive test - such as an eye test - could be a significant step forward in the search for treatments that can tackle the underlying causes of the condition rather than masking its symptoms,” he added.

The BBC reported that the team found that a newly formulated version of drug normally used to treat diabetes led to less cell damage.